The present invention relates to a new and improved construction of a grinding apparatus for fibres contained in a stock suspension for use in the paper industry, especially for the fabrication of paper.
Generally speaking, the grinding apparatus of the invention is of the type comprising a housing within which there is rotatably mounted a rotor equipped with at least one grinding tool set and possessing a wall portion or part equipped with a second grinding tool set. In order to adjust the grinding gap between both of the grinding tool sets one of the parts carrying the grinding tool sets is moveably guided in relation to the other part in axial direction of the rotor towards such other part and away from the latter and can be adjusted by means of a piston-and-cylinder unit or device which can be impinged with a pressurized fluid medium. The piston-and-cylinder unit contains a contact or pressing chamber which is effective in the sense of bringing together or having the grinding tool sets approach one another and a lift-off chamber which is effective in a lift-off direction for shifting apart the grinding tool sets.
According to a prior art grinding apparatus of the afore-mentioned type, as disclosed in German Pat. No. 2,146,548 and the corresponding U.S. Pat. No. 3,810,584, granted May 14, 1974, the piston-and-cylinder unit contains an auxiliary or additional piston which is not connected with the main piston and can be axially displaced and fixedly positioned in relation to the main piston. This auxiliary piston forms a stop or impact member which limits the adjustment movement of the moveable part of the piston-and-cylinder unit in a direction corresponding to bringing together of the grinding tool sets or fittings. The cylinder chambers of this known grinding apparatus are connected with a hydraulic actuation system, by means of which there can be impinged with the momentarily required pressure each of the cylinder chambers or spaces. The actuation of the auxiliary piston requires a separate control arrangement which must be supervised or monitored. Standing in opposition to the known equipment design is the requirement that there be afforded as simple as possible construction of the grinder apparatus, and in this respect there is strived for a design having as few as possible moveable, robust and easily exchangeable components.